The Reibergram for immunoglobulin A in dogs: Evaluation of intrathecal IgA synthesis using a quotient graph in dogs with neurological diseases

Abstract Background Increased cerebrospinal fluid (CSF) protein concentration is a common finding in neurological diseases of dogs. Distinguishing between intrathecally‐produced proteins and proteins that have passed the blood‐CSF barrier because of barrier disruption facilitates diagnosis. Albumin is a microprotein mainly produced extrathecally that can be used as a reference marker for blood‐CSF barrier dysfunction. Objectives Develop a quotient graph based on the CSF/serum quotient of albumin and immunoglobulin A (IgA; Reibergram) to visualize intrathecal IgA synthesis and blood‐CSF barrier dysfunction. Animals and Methods Retrospective single‐center cohort study. A hyperbolic function was developed using data from 6 healthy Beagles and 38 dogs with neurological diseases in which an isolated blood‐CSF barrier dysfunction was expected. The function was validated using data from 10 dogs with expected intrathecal IgA synthesis and was visualized as a quotient graph. Finally, the graph was used to evaluate data of 118 dogs with various neurological diseases. Results Within the Reibergram, the function QLimIgA=0.13QAlb2+11.9·10−6−1.01·10−3 describes the upper values of physiological IgA quotients. It detects diseases with expected intrathecal IgA synthesis with higher sensitivity (85%) and specificity (89%) than the IgA index. The upper value of the physiological albumin quotient is 2.22 and detects diseases with expected blood‐CSF barrier dysfunction (sensitivity: 81%; specificity: 88%). Conclusion and Clinical Importance The canine Reibergram can detect blood‐CSF barrier dysfunction and intrathecal IgA synthesis in the majority of cases. The graphical visualization simplifies data evaluation and makes it a feasible tool in routine CSF diagnostic testing.